Analysis of toxic load calculations and fluctuation concentrations modeling for the assessment of atmospheric accidental release

Abstract : Computing the effect zones around industrial facilities requires using modelling tools. For the specific case of accidental scenarios involving toxic cloud dispersion, it is necessary to make use of acute toxicity threshold values. Those thresholds can be given in terms of concentration or in terms of toxic load. The toxic load is commonly evaluated by extensions of the Haber's law that corresponds to an integration in time of concentration. The improvements achieved in the atmospheric dispersion modelling now enable to predict the intermittency of the toxic cloud. However, such new approaches raise questions about the relevance of the toxic load evaluation, knowing that many parameters which characterize biological reality and the whole process of the dose-response should be taken into account. To achieve a deterministic model, it is necessary to pool research efforts between the communities of toxicologists and the atmospheric dispersion modellers. This paper consists in confronting the level of knowledge of the fluctuation toxic cloud and biological parameters in the context of the deterministic modelling of consequences generated by an accidental toxic cloud.